This description relates to a class of aircraft that use rotary wings (rotors) for lift such as a helicopter/multicopter, gyrocopter or gyrodyne aircraft.
A gyrodyne aircraft consists of a fuselage with one or more propulsion power sources (ICE jet/propeller), one or more rotors that provide additional powered lift during vertical takeoff and landing and often fixed wings and/or standard aircraft control surfaces for normal cruise flight. These rotors are basically unpowered during the balance of the flight and may be the sole lifting surfaces by autorotation, be used to augment the lift of other winged surfaces or be slowed to reduce drag while relying mostly/solely on the lift of other winged surfaces. Autorotation is an aerodynamic state of a rotor where the only power applied to the rotor is from the airflow through the rotor, which provides the rotational power, and the resulting rotation of the blades provides lift.
The purported advantage of a gyrodyne versus a helicopter is to provide a less complex vertical lifting system generally not requiring the expensive variable pitch rotors and complex maintenance-prone swash plate for collective and pitch control while providing a higher cruise speed. Higher cruise speed is accomplished by using separate dedicated propulsion engines with reduced drag by relying on other wing surfaces and/or reduced RPM of rotor surfaces.
While any number of rotors can be used in a gyrodyne, historically it has been just one rotor. Gyrodynes that use one rotor do not typically require a compensating torque device such as the tail rotors found on helicopters because torque is not applied between the aircraft and the rotor in flight. For example, ram jets on the wing tips were used on the 1950-60's Fairley Rotodyne and similarly tip jets in the early 2000's DARPA-Groen Brothers Heliplane project. The Carter Copter uses a high inertia rotor at a flat (no lift) pitch spun up on the ground (due to friction with the ground the applied torque will not spin the aircraft. Then the spin force (torque) is disconnected, the pitch is quickly increased resulting in a high “jump takeoff” lift for a short period of time while the aircraft transitions to forward flight. For landing, the rotor is set to high RPM by autorotation during the approach and the inertia of the rotor provides enough energy to provide a pitch controlled soft/vertical landing.
Autorotation is also used to provide lift as an emergency landing method for helicopters in the event of power failure to the rotor(s).